The present disclosure relates to toner compositions with toner particles having a core-shell type structure and antiplasticizers in the core and/or shell. More particularly, embodiments herein relate to hybrid toner compositions.
Hybrid toners having some of the polyester resin latex replaced by a styrene/acrylate latex is a key in facilitating future cost reduction for certain toner products. For example, hybrid toners may contain a styrene/acrylate shell and a core comprising a styrene-acrylate copolymer and amorphous polyester. By replacing the polyester with more styrene/acrylate copolymer, the cost is reduced as polyester is traditionally a more expensive material. Not only are the polyester raw materials generally more expensive, but to prepare polyester latex to enable use in emulsion-aggregation toner requires an additional processing step, which often requires the use of solvents, verses styrene/acrylate copolymers can be directly prepared as a latex when the resin is prepared by emulsion polymerization. However, it was discovered that toners with styrene-acrylate latexes do not melt at the same temperature during the toner process as the polyester toners, thus leading to variation in the surface morphology in a hybrid of the two toner types (more polystyrene/acrylate remains on the surface). For example, a polyester emulsion/aggregation toner prepared by a batch process is generally coalesced at temperatures from about 70° C. to about 86° C., for example, US patent application 20150056551, while a styrene/acrylate toner is generally coalesced at temperatures above 90° C., typically from 95 to 96° C., as for example in U.S. Pat. No. 7,645,551, herein included by reference.
A potential approach to address this mismatch is to elevate the coalescence temperature in the EA process from the conventional coalescence temperature of 85° C., but increasing the coalescence temperature cause pigment coagulation to take place and results in dielectric loss. This is because, especially for hybrid toners where the core contains both styrene/acrylate resin and polyester resin, the pigment (e.g., carbon black for black toner) preferentially situated in the polyester resin portion of the toner or in the interface of the styrene/acrylate and polyester, and therefore is unable to disperse into the styrene/acrylate resin portion of the toner. With less polyester presented in the toner due to the replacement with styrene/acrylate, the local concentration of the carbon black increases, leading to a higher chance that carbon black particles are in contact with one another, thus increases the conductivity of the toner as measured by dielectric loss. Therefore, such poor pigment dispersion leads to high dielectric loss, which in turn leads to poor transfer efficiency in the printer, and, in some cases, lower charge as well. Reducing the coalescence temperature in polyester toners may reduce the dielectric loss, but once styrene/acrylate is added to the polyester core emulsion, the coalescence temperature is required to be raised to ensure a fully coalesced styrene/acrylate shell.
It is found that the polyester portion of the hybrid toners has a lower viscosity and higher molecular mobility compared to the styrene/acrylate portion. This results in incompatibility of the polymers causing pooling or large domains of the same polymer material (i.e., poor intermolecular mixing) within the toner particle, therefore causing poor distribution of the carbon black and possibly the wax (release aid).
The inventors of the present disclosure discovered that by including an antiplasticizer, such as a low molecular weight organic material, can help antiplasticize the polymers, and thus can solve the aforementioned problems.